It has been proposed previously to make cellulose solution using the NMMO hydrates as follows.
U.S. Pat. Nos. 4,142,913, 4,144,080 disclose manufacturing methods for making cellulose solution by obtaining cellulose solution by under reduced pressure distillation of cellulose that is swelled and dispersed in NMMO hydrates, solidifying the cellulose solution to a precursor (solid-state) by cooling the cellulose solution(a kind if ‘making chips’) and melting in an extruder. These methods simplify the melting process by using an extruder, but require relatively long time and a large amount of energy because of the preceding ‘making chips’. And also, the precursor is hard to protect from heat and humidity.
U.S. Pat. No. 5,584,919 discloses a manufacturing method for making cellulose solution by preparing solid-state NMMO comprising 5 to 17% by weight water, feeding the solid-state NMMO with cellulose powder into a horizontal cylinder-type high speed mixer and mixing them to make a granule type precursor, and melting the precursor using an extruder. This method, however, has a disadvantage of a wide distribution of the obtained the precursor and low yield. If the volume of the raw material is larger, the distribution of the obtained precursor is more widened. And a complicated cooling apparatus is required to transfer and store the precursor. And also, the solid-state NMMO is hard to manufacture and store.
U.S. Pat. Nos. 5,094,690, 5,534,113 and 5,603,883 disclose a manufacturing method for making cellulose solution by dispersing cellulose in the NMMO comprising 40% by weight water to make slurry, removing the water from the slurry by using a Force-drive type thin-layer distillation apparatus that can form a thin, solution-layer, and obtaining the cellulose solution. These methods, however, have disadvantages of a low efficiency to the volume of the raw material because the slurry was distilled the water and melted by rotating of the rotor so slurry was downstreamed. It caused a short dwelling time in the above apparatus. And also, these methods require a relatively long time and relatively a large amount of energy to produce cellulose solution, and the obtained fiber using the above cellulose solution gets worse the tenacity by degradation of cellulose and change of color of the NMMO.
U.S. Pat. Nos. 5,421,525, 5,456,748, 5,534,113 and 5,888,288 disclose manufacturing methods cellulose solution by mixing pulp crashed into irregular flat type with NMMO comprising 22% by weight water in a horizontal cylinder-type mixer and swelling them, swelling again by stirring for hours in a storage hopper, removing the water form the high viscid solution by using a Force-drive type thin-layer distillation apparatus so as to obtain the melted cellulose solution. These methods, however, have a disadvantage of extra handling and feeding of dust pulp produced as by-product during when crash the pulp into irregular flat type pulp. And also, it is hard to operate the horizontal cylinder-type mixer to discharge the swelled solution. In U.S. Pat. No. 5,921,675 discloses a horizontal cylinder-type mixer comprising a conveyor screw at the outlet of the mixer.
U.S. Pat. No. 5,948,905 discloses a manufacturing method for making cellulose solution by distilling the water from a mixture of cellulose and NMMO hydrates comprising about 23% by weight. In this method, the mixture was distilled under reduced pressure during passing the nozzle having 1.5 to 6.0 millimeter diameter. It is composed of multi-stage chambers. The first-stage chamber has a small number of nozzles having relatively large diameter. As the chamber's stage is increased, the number of nozzle is increased and the diameter of the hole of the nozzle is decreased so as to increase the cross-sectional area in order to upgrade the efficiency of water vaporization. At the stage of eighth, the last stage, an extruder is used. This method, however, has a disadvantage of needing of a highly complicated apparatus that is composed of many chambers different each other and comprised too many screws for shifting the chambers and distilling stages.
PCT WO 1997/47790 discloses a manufacturing method for making cellulose solution by solving cellulose powder in the liquid-state NMMO directly in a twin-screw type extruder. The cellulose solution is produced by feeding the liquid-state NMMO comprising 12% by weight water into the first barrel of the extruder maintaining an inner temperature of 100° C., feeding cellulose powder into the third barrel of the extruder maintaining an inner temperature of 75° C., shifting and mixing them, and obtaining the solution by rising the temperature to 120° C. In this method, however, three barrel of the extruder is used for feeding the cellulose powder and NMMO, and another barrel is required for melting the cellulose. In fact, there is a relatively short swelling zone so as to obtain cellulose solution comprising not-liquified cellulose particles. So, this method is effective to proceed relatively small amount of raw material, however, it is not proper to adapt a mass production of cellulose solution because there are too many not-liquified moiety. And it is not proper economically because of requiring a lot of filter system. And also, this method has a disadvantage of too short spinning cycle. If the swelling zone of the extruder is increased by increasing the number of blocks and the L/D(length/diameter) of the screw, it is hard to control the swelling condition and the melting condition concurrently because the screws of the extruder are driven by single driving shaft.
Korean patent application laid-open publication No. 2002-24689 discloses a manufacturing method for making highly homogenized cellulose solution by obtaining a mixture of swelled cellulose pulp powder and liquid-state NMMO by using the liquid-state NMMO that is overcooled by cooling air and melting the mixture. This method, however, is hard to control the temperature of the overcooled NMMO by using the cooling air and to control the content of the NMMO because of exposing of the moisture contained in the cooling air.
After being disclosed in U.S. Pat. No. 2,179,181 granted to Graenacher and Sallman(1939) and the British Pat. No. 1,444,080 granted to Johnson tertiary amine oxide as the one of the most powerful solvent for solving cellulose, there are many patent and literature disclosed the using of the solvent. And NMMO is the most popular solvent among tertiary amine oxide. The oxygen of the N—O group, active moiety, of the NMMO can form a inter-molecular linkage with hydroxy group of a material such as cellulose so as to penetrate easily in the crystalline structure of the cellulose. Chanzy et al. subscribed that there are some differences of reaction activation according to the extent of hydration of the NMMO and temperature.